1. Field of the Invention
The invention is related to the field of magnetic disk drives, and in particular, to performing a droplet removal process to dissipate liquid droplets that form on a slider in a magnetic disk drive.
2. Statement of the Problem
Many computer systems use magnetic disk drives for mass storage of information. Magnetic disk drives typically include one or more sliders having a read head and a write head. An actuator/suspension arm holds the slider above the surface of the magnetic disk. When the magnetic disk rotates, an air flow generated by the rotation of the magnetic disk causes an air bearing surface (ABS) side of the slider to fly a particular height above the magnetic disk. As the slider flies on the air bearing, a voice coil motor (VCM) moves the actuator/suspension arm to position the read/write head over selected tracks of the magnetic disk. The read/write head may then read data from or write data to the tracks of the magnetic disk.
As the density of magnetic disks increases, it has become more important to precisely control the spacing between the read/write head and the surface of the magnetic disk. The spacing between the read/write head and the surface of the magnetic disk is often referred to as the fly height of the read/write head. One factor contributing to the fly height is the shape of the ABS of the slider and the rotational speed of the magnetic disk. Another factor contributing to the fly height is the amount of protrusion of the read/write head toward the surface of the magnetic disk.
The read/write head is fabricated from materials that are different than the rest of the slider body. These materials expand and contract at different rates than the slider body. Thus, disk drive manufacturers take advantage of these material properties by embedding one or more heating elements in the read/write head or proximate to the read/write head. The protrusion of the read/write head may thus be precisely controlled by the application of a heating power to the heating element. Controlling the protrusion of a read/write head through the application of a certain heating power to the heating element is referred to herein as Thermal Fly-height Control (TFC).
As the slider flies over the surface of the magnetic disk, the slider may collect a lubricant that is deposited on the surface of the magnetic disk, or may collect other liquids that condense from vapors in the magnetic disk drive. Air flow over the slider surfaces then causes these liquids to accumulate as liquid droplets on low pressure points of the slider. The low pressure points are typically on the ABS of the slider, or on the trailing end of the slider. When the liquid droplets grow to a sufficient size, they can detach from the slider and fall onto the surface of the magnetic disk. If the slider subsequently comes into contact with the liquid droplet, such as on the next revolution of the magnetic disk, the liquid droplet may cause the slider to “jump” temporarily. If the read/write head is in the process of performing a read/write process when the slider jumps, then the data being read or written may be corrupted. Thus, it would be advantageous to remove these liquid droplets from the slider before the liquid droplets fall onto the surface of the magnetic disk.
One solution to the problem is to heat the slider while the slider is in an operating position. The heating of the slider can cause the liquid droplets to dissipate before they fall onto the surface of the magnetic disk. Unfortunately, the air flow caused by the rotation of the magnetic disk and the thermal transfer of energy from the slider to the magnetic disk affects the heating of the slider. It may thus take more power than desired to heat the slider enough to dissipate the liquid droplet.
Another solution to the problem is to heat the slider through the write head in the slider. Because the write head is formed from a coil having a low resistance, it may again take more power than desired to heat the slider enough to dissipate the liquid droplet.
Yet another solution is to stop the rotation of the magnetic disk, and to land the slider on the surface of the magnetic disk. Such a process of landing the slider on the stationary magnetic disk is traditionally referred to as Contact Start-Stop (CSS). When the slider is parked on the surface of the magnetic disk, a current is passed through the slider body which in turn heats the whole slider. The heating of the slider helps to dissipate the liquid droplets that have accumulated. Unfortunately, heating the slider while it is parked on the surface of the magnetic disk may be harmful to the magnetic disk. Also, passing a current through the entire slider body can damage some components in the slider.